North Korean leader Kim Jong-un and officials take a group tour through a machinery production facility in Pyongyang on Monday. (Yonhap)

North Korea fired two short-range missiles into the sea off its east coast Monday, Seoul's defense ministry said, in its latest provocation seen as a reaction to the ongoing joint military drills between South Korea and the United States.

One missile was fired from the Gitdaeryeong area and the other from Wonsan, both on the North's southeastern coast, in the northeast direction beginning at 6:19 a.m.

"The missiles are evaluated to have flown over 500 kilometers," ministry spokesman Kim Min-seok said in a briefing, adding they were believed to be of the Scud-C type.

It is the second such launch of the short-range missiles in a week. Last Thursday, Pyongyang fired four Scud missiles from the same area, which flew about 220 km in a northeast direction.

The latest unprovoked firings came as South Korea and the U.S. have been conducting annual joint military exercises that Pyongyang has condemned as a rehearsal for an invasion of the communist nation. On the first day of the Key Resolve drills last week, the North briefly violated the tense western sea border three times.

"North Korea is taking a two-faced approach, showing the reconciliatory peace gesture on the surface, while launching provocations on the other hand," the spokesman said in a briefing. "We sound a serious warning to North Korea, urging it to stop provocations."

Kim said Pyongyang's missile launches are a violation of U.N. Security Council resolutions that ban use of the ballistic missile technology, though the missiles were fired into its territorial waters.

"In light of the border trespassing and short-range missile launches, South Korean and U.S. forces have stepped up their surveillance status to closely watch the North Korean military's latest moves," Kim said. "We are ready to strike back if provoked."

Experts estimate that the North has over 700 Scud-B and Scud-C missiles, recently deploying Scud-ER, with a range of more than 700 km and improved accuracy. The communist regime has also pursued the development of long-range missiles that can reach as far as the continental U.S.

Seoul officials have raised concerns that the missile launches could hamper the reconciliatory mood between the two Koreas following the reunions of families separated by the 1950-53 Korean War at the North's Mount Kumgang resort in late February.

"Considering that the North fired the missiles into the sea, it is deemed a low-level provocation," a senior military official said, asking for anonymity. "But it is worrisome that (the missile launch) could negatively affect inter-Korean relations when hopes

are high for better ties in light of the family reunions."

The two-week Key Resolve is a computer-based command post exercise, which ends Thursday, while combined field training Foal Eagle, involving 7,500 American troops, runs through April 18.

Amid the warming inter-Korean ties, Seoul and Washington have been staging relatively low-profile exercises this year so as not to provoke the North, but their drills have nevertheless drawn fierce criticism from the communist state.

Pyongyang had issued near-daily threats during last year's joint drills that were held following its third nuclear test, prompting the U.S. to send high-profile nuclear bombers and stealth jets to the Korean Peninsula in a show of force.

On Monday, the North's state-run Rodong Sinmun denounced Washington for raising tensions on the peninsula by holding the Key Resolve and sending the B-52 bombers last year.

"The United States is stepping up military provocations, going against the tide of peace and eased tension on the Korean Peninsula," said an editorial carried by the paper. "The U.S. does not welcome improved inter-Korean ties and is conducting all forms of maneuvers to intensify confrontations between the two Koreas."

Amid rising tensions, U.S. nuclear-powered submarine USS Columbus and the 7th Fleet flagship USS Blue Ridge arrived at the southeastern port city of Busan earlier in the day to participate in the joint exercises with South Korea.

About 28,500 U.S. troops are stationed in South Korea to help deter North Korean aggression. South and North Korea remain technically in a state of war as the Korean War ended in a ceasefire, not a peace treaty. (Yonhap)